Alkali metal generating agents

ABSTRACT

ALKALI METAL GENERATING AGENTS GENERALLY USED IN FORMING A PHOTOSENSITIVE LAYER, CHARACTERIZED IN THAT THEY CONSIST OF A MIXTURE OF ALKALI METAL SALTS AND NIOBIUM. THE MIXTURE IS PUT IN A VESSEL MADE OF ELECTRIC CONDUCTIVE MATERIAL TO FORM A GENERATOR. WHEN THE GENERATOR IS HEATED BOTH MATERIALS REACT WITH EACH OTHER TO ALLOW THE ALKALI METAL TO COME OUT OF THE VESSEL AND FORM THE AFOREMENTIONED LAYER.

April 1 2 YORIKATSU IRISAKA ETA}. 3,658,713

ALKALI METAL GENERATING AGENTS Filed Nov. 10, 1969 9 Sheets-Sheet lNb+Cs2CrO4 Zr+Cs2CrO4 3 Si+Cs2CrO4 '5 s 1 i ii LL O z 3 O 2 4TEMPERATURE(C) April 25, 1972 YORIKATSU IRISAKA ET AL 3,658,713

ALKALI METAL GENERATING AGENTS Filed Nov. 10, 1969 9 Sheets-Sheet 2TEMPERATURE (c) Ap 25, 2 YORIKATSU IRISAKA ETAL 3,658,713

ALKALI METAL GENERATING AGENTS Filed Nov. 10, 1969 9 Sheets-Sheet a FIG.2A

8 X160)% muoowa 00000 OF GOOD PRODUCTS ST REPRODUCIBILITY N0.

Nb/K2Cr04 RATIO BY WEIGHT FIG. 20

NO. OF TESTS REPIRODUCIBILITY (NO- OF 6000 PRODUCTS Nb/C s2CrO4 RATIO BYWETGHT April 25, 1972 YORIKATSU IRISAKA ET AL 3,658,713

ALKALI METAL GENERATING AGENTS Flled Nov. 10, 1969 9 Sheets-Sheet 4060000 CQIDQ'YON- 001x SiSELL 50 ON AlI'IIQIOHGOHdBH SiOfiCIQHfi April25, 1972 Filed NOV. 10, 1969 K AMQUNT OF GENERATION (mg) Na AMOUNT OFGENERATIOMmg) YORIKATSU IRISAKA ET AL 3,658,713

ALKALI METAL GENERATING AGENTS 9 Sheets-Sheet 5 6 F|G.3A

TEMPERATURE(C) FIG,3B

TEMPERATURE(C) April 1972 YORIKATSU IRISAKA ET AL 3,658,713

ALKALI METAL GENERATING AGENTS Filed Nov. 10, 1969 9 Sheets-Sheet 6TEMPERATURE OF GEMRATIONPC) WNW/Nb 0F MIXTURE L FLIG.5A

Cs AMOUNT OF GENERATIOMmg) TEMPERATUREPC) April 25, 1972 Y-ORIKATSUIRISAKA ET AL 3,653,713 I ALKALI METAL GEZ ERATING AGENTS Filed Nov. 10.1969 9 Sheets-Sheet 7 T FIG. 5

A 5 5 Q E 2 0.3 m o 5 0.2-

.01 o E 4 V v x I I V .L I

- TEMPERATURE(C) FIG. 6

TEMPERATURE OF GENERAT|ON(C) April 25, 1972 Filed NOV. 10, 1969 CsAMOUNT OF GENERATION 1111 No AMOUNT OF GENERATIOMmg) YORIKATSU IRISAKAET AL 3,658,713

ALKALI METAL GENERATING AGENTS 9 Sheets-Sheet 8 FIG. 7A

TEMPERATURE (C) TEMPERATUREPC) A ril 25, 1972 Filed Nov. 10, 1969TEMPERATURE (c) YORIKATSU IRISAKA ET AL 3,658,713

ALKALI METAL GENERATING AGENTS 9 Sheets-Sheet 9 MIXTURE 0.01 0.1 10 mom.RATIO ((EfiNQ/Nb 0F United States Patent 01 ice 3,658,713 Patented Apr.25, 1972 US. Cl. 252-181.4 Claims ABSTRACT OF THE DISCLOSURE Alkalimetal generating agents generally used in forming a photosensitivelayer, characterized in that they consist of a mixture of alkali metalsalts and niobium. The mixture is put in a vessel made of electricconductive material to form a generator. When the generator is heatedboth materials react with each other to allow the alkali metal to comeout of the vessel and form the aforementioned layer.

The present invention relates to alkali metal generating agents and moreparticularly to said agents put in a vessel made of electric conductivematerial so as jointly to form an alkali metal generator.

Alkali metal generating agents heretofore used in forming thephotoconductive target or surface of a special tube such as an imagepickup tube or photoelectric tube consist of a mixture of a single orplurality of alkali metal salts and a single or plurality of reducingagents. The mixture is received in a vessel made of electric conductivematerial and perforated with a plurality of small bores to form agenerator.

There are selectively used various kinds of alkali metal salts accordingto the type of a photosensitive layer employed. The known types of saidsalts include chromates, bichromates, tungstates and molybdenates ofsodium, potassium, cesium, lithium and rubidium. And the known types ofreducing agents are mainlysilicon, zirconium, aluminum and boron.

Such prior art alkali metal generator is previously disposed in theprescribed part of a tube at which there is to be formed aphotosensitive layer. Where it is required to form said layer, the metalvessel is heated by introduction of current or high frequency inductionfor reaction betweenthe alkali metal salts and reducing agents so as torelease alkali metals. The alkali metal thus released is deposited onthe surface of a photoelectric substrate, for example, an antimony filmpreviously conditioned for this purpose by maintaining a part of thetube at a suitable level of temperature, thereby forming aphotosensitive layer or surface through a further prescribed process.

The aforementioned metal vessel is fabricated by rolling a thin electricconductive sheet in the transverse direction, to form a hollowcylindrical body, spot welding the superposed edge portions at aplurality of points arranged in the longitudinal direction at aprescribed interval and finally closing up an opening at both ends ofthe hollow cylindrical body by pressure. The aforesaid spot welding isintended to allow the released alkali metal to be drawn out of thevessel through the gaps formed between the welds.

With the prior art alkali metal generator having the aforesaidarrangement, it is required to heat the generator up to the temperatureat which there occurs the exothermic reaction of the above-mentionedmixture in order to release a relatively large amount of alkali metalfrom a given amount of alkali metal salt used. However, heating of thegenerator to such high level of temperature leads to a rapid occurrenceof reaction, thuspresepting difliculties in controlling the amount ofalkali metal to be released.

To prevent such rapid occurrence of reaction, the prior art addstungsten as a buffer agent to mixtures of alkali salts and reducingagents. However, even addition of said tungsten failed reliably tocontrol the aforementioned rapid reaction. Accordingly, a photosensitivelayer obtained by the prior art could not display a desired degree ofphotosensitivity, nor was fully satisfactory in other respects.

It is accordingly the object of the present invention to provide analkali metal generating agent capable of easily controlling the velocityof exothermal reaction which raised a problem with the prior art, byadding niobium as a reducing agent to the alkali metal salt and forminga photosensitive layer or surface having excellent properties and alsoan alkali metal generator prepared by putting said generating agent in avessel made of electric conductive metal.

This invention can be more fully understood from the following detaileddescription when taken in connection with reference to the accompanyingdrawings, in which:

FIGS. 1A and 1B are diagrams comparing the amount of alkali metalreleased from the prior art alkali metal generating agents correspondingto the associated temperature with that of a similar agent according toan embodiment of the present invention;

FIGS. 2A to 2C illustrate the effect of a kind of alkali metalgenerating agent according to the invention and the relationship of theyield of alkali metal in forming a photosensitive film versus the ratioin which there are blended the components of said agent;

FIGS. 3A and 3B are similar diagrams to FIG. 1A comparing the alkalimetal generating property associated with Example D of the inventionwith those of the prior art alkali metal generating agents;

FIG. 4 is a diagram indicating the relationship between the blendingratio of an alkali metal salt and niobium constituting the generatingagent used in said Example D and the temperature required for saidgeneration;

FIGS. 5A and 5B are similar diagrams to FIGS. 3A and 3B associated withthe alkali metal generating agent of Example E;

FIG. 6 is a similar diagram to FIG. 4 associated with Example E;

, FIGS. 7A and 7B are similar diagrams to FIGS. 5A and 5B associatedwith the alkali metal generating agent of Example F;

FIG. 8 is a similar diagam to FIG. 6 associated with Example F; and

FIG. 9 is a perspective view, with part broken away, of an exampe of analkali metal generator filled with the generating agent of theinvention.

For better understanding of the present invention, there will now bedescribed the prior art reducing agents. Reaction of the prior artreducing agents such as silicon, aluminium and zirconium with alkalimetal salts is of exothermic type. Among said reducing agents, siliconcauses a tremendous evolution of heat. And all these reactions, exceptbetween cesium chromate and zirconium, take place very rapidly. Evenaddition, as heretofore attempted, of powdered tungsten as a bufferagent for suppressing the above-mentioned rapidity of reaction fails tocontrol reaction velocity with respect to other alkali metal generatingagents than a mixture of zirconium and potassium chromate. Although amixture of zirconium and alkali metal salts allows its reaction velocityto be appreciably controlled as described above, there will most likelytake place an explosion during reaction, so that said mixture is barredfrom use. Where the aforementioned both components are slowly mixed dryin the forming of relatively coarse powders, said explosion may beavoided Yield alkali metal (percent) ca. 80 ca. 30 w TABLE 1 Tempera-Generated state Phototure of afiected by Gas evolution gener- Puncturevarying prebefore gener- Control of Getter True Bulk lOSSlbll- Mixingtivrty, Generated atron, or breakage heating ation of alkali generatedaction of density density Addition of lty of l'atlo [IA/[3111.2 state C.by melting conditions metal state reduetant (g./em. (g./em. butter agentexplosion 100 Very stable-- ca. 780 Never Little afieeted Very smallEasy.. Great"..- 6.42 2.4 Unnecessary None 50 U stable..- ca. 900Sometimes Notfiieeably Prominent DiIficult Small 2. 745 0.9Necessary......... -.d a eeted. ca. 900 Quite rare." Affected. Fairlynoticeable Fairly easy Great ca. 800 Never Little aileotednl" Verysmall- Mixture Nb-l-CsrCrO4 to a certain extent. However, such processdoes not afford uniform mixing, nor does use of coarse powders assist inthe reduction of the surface area of zirconium taking part in reaction.Accordingly, if it is desired to generate a 5 prescribed amount ofalkali metal, it is necessary to use a large amount of the aforesaidmixture. On the other hand, wet mixing of zirconium and alkali metalsalts can indeed prevent the occurrence of an explosion. But the alkalimetal salt is dissolved in water to become ueseless. Even where alcoholis used in place of water, minute amounts of water contained in thealcohol denature the alkali metal salt and the segregation of said saltin the subsequent drying process reduces the uniformity of said mixture,thus failing to form a satisfactory photosensitive layer.

The prior art alkali metal generator is generally preheated to minimizethe evolution, during reaction, of unnecessary gases from the alkalimetal salts, reducing agents and metal vessel used. However, saidpreheating has the drawback that there are evolved during reactiondifferent amounts of such unnecessary gases from a mixture of an alkalimetal salt and silicon or zirconium, depending on the condition in whichsaid preheating is conducted.

Heretofore, there has been further proposed a different type of analkali metal generator capable of generating appreciable amounts ofalkali metal at relatively low temperature, wherein there are addedpowders of tunsten and boron to a mixture of alkali metal salts andreducing agents. Even this generator, however, presents difiiculties incontrolling reaction velocity.

The different properties of the prior art alkali metal generatingmixture and the mixture of the present inven tion which typicallyconsists of alkali metal salts and niobium are presented in FIGS. 1A and1B and Table 1 below. The ordinate of the figures represents the amountof alkali metal generated (the ordinate of FIG. 1A denotes cesium andthat of FIG. 1B potassium) and the abscissa indicates heatingtemperature C.).

Table 1 does not include an alkali metal gencrating agent containingaluminium as a reducing agent. Such generating agent resembles thosecontaining silicon and zirconium in respect of property, but evolvestremendous amounts of gas during reaction, failing to provide a goodphotosensitive layer. 'On the other, use of scale-like pieces ofaluminium can indeed suppress gas evolution to a certain extent, butthere is required an extra process of working aluminium itself into suchscale-like pieces.

There will now be described the present invention in greater detail. Itis preferred that powders of alkali metal salts and those of niobiumfilled into a vessel made of electric conductive metal from which alkalimetal is released be mixed in the ratio by weight ranging from 1:0.1 to8. The reason is that in the ratio of lzless than 0.1, the content ofniobium is too small to display its expected effect, whereas in theratio of 1:lnore than 8, there likely takes place a rapid exothermicreaction. Further speaking of the effect caused by the content ofniobium.

(A) Where the alkali metal salt consists of potassium chromate (K CrO itis advisable to mix it with niobium in the ratio by weight of about1:0.1 to 8 (or in the mol ratio of about 1:0.23 to 18.4), preferably inthe ratio by weight of about 1:0.3 to 4 (or in the mol ratio of about1:0.69 to 9.2). The mol number of alkali metal represents that of saltsthereof. Hereinafter, the mol number of alkali salts is expressed bydrawing a bar above symbols representing alkali elements, as l\ a, K"Cs. The mol number of for example, Na CrO or K WO is denoted as fia orTi. This is derived from the fact that where there was manufactured aphotoelectric tube using an alkali metal generating agent whosecomponents were mixed in the forming ratio, the yield of alkali metalaccounted for about 90 to 100 percent and in the case of the lattermixing ratio approximately 100 percent.

(B) Where the alkali metal salt consists of cesium chromate (Cs CrO itis desired that said salt be mixed 52 1.8 Preierred. Present 7 2.1Unnecessary 5 0.9 Necessary do 4.44 1.2 Preferred Present. 11.95 3.1Already contained" None 8.75 2.1 do Present 2:1 60 Stable 2:1 Verystable Easy l.do.

2:1 Unstable ca. 900 Sometimes Nogeeibiy Prominent... Difficult...Sma1l-- a co e 2:1 Stable ca. 900 Quite rare Atteered Fairly noticeable"Fairly easy. Great..

2:1 .do ca. 900 Sometimes do Prominent d0.- Sma1l..

2:1 do ca. 900 Quite rare do do, ...d0.- Great.

with niobium in the ratio by weight of about 1:03 to (or in the molratio of about 1:1.21 to 40.49), preferably in the ratio by weight ofabout 1:05 to 3 (or in the mol ratio of about 1:2.02 to 12.12).

(C) In case sodium chromate is used as an alkali metal salt, theadvisable ratio by weight of said salt to niobium is about 1:01 to 10(or about 1:0.19 to 19 in the mol ratio).

There was formed a photosensitive layer from the aforesaid alkali metalsalts, i.e., potassium chromate, cesium chromate and sodium chromatemixed with niobium in varying proportions, the yield of alkali metalbeing presented in FIGS. 2A, 2B and 2C respectively. Throughout thesefigures, the ordinate represents the percentage yield of alkali metal orreproducibility (number of good products/num'ber of tests X100) and theabscissa denotes the ratio by weight of niobium to the aforementionedalkali metal salts.

As described above and indicated'in Table l, the alkali metal generatorof the presentinvention allows alkali metal to be released at atemperature about 100C. lower than required for the prior art, reducesthe evolution of unnecessary gas, eliminates the necessity of -.usingany special buffer agent and easily controls reaction velocity becausereaction does not occur rapidly. Moreover, the generated state of alkalimetal does not Widely vary with changes in the conditions in whichpreheating is conducted prior to application of heat for reaction, andon this account, too, reaction velocity can be easily controlled. Thefact that the photosensitive'layer prepared from the alkali metalgenerating agent of the present invention is elevated about 70 percentin photosensitivity over the prior art layer evidently proves that saidagent is prominently excellent with respect to the aforementionedrequirements.

The alkali metal generator of the present invention further offers theundermentioned favourable effect. The alkali metal generating agent ofthe invention generally has a greater bulk density than the prior artagent (for example, where the alkali-metalsalt consists of cesiumchromate and there is added niobium thereto as claimed in the presentinvention, the entire mass has a bulk density of 2.4 g./cm. whereas theprior art agent containing silicon amounts to 0.9 g./cm. in bulk densityand that containing zirconium to 1.8 g./cm. This means that the alkalimetal generating agent of the present invention has a bulk density about25 timesthat of the prior art siliconbearing agent and about 1.3 timesthat of the prior art zirconium-containing agent). Accordingly, thealkali metal generating agent of the present invention can be reduced inbulk, permittinga vessel of electric conductive metal to be madecompact. Also the fact that relatively small amounts of said alkalimetal generating agent are used and reaction can proceed at a relativelylow temperature naturally decreases the evolution of unnecessary gasduring the exothermic reaction. Furthermore, the present alkali metalgenerating agent enables alkali metal to be released ina prominentlyelevated yield. Though the reason is not fully understood, it is assumedthat the intermediate product probably formed by reaction betweenniobium and the alkali metal generating agent islessliable to obstructthe release of alkali metal than the intermediate product supposed tooccur during the reaction of the prior art alkali metal generatingmixture.

For illustration of other. combinations of alkali metal potassiumtungstate (K WOQ and. niobium. mixed in different ratios as given below.

In any of the above ratios, the present invention displayed its claimedeffect of easily controlling reaction velocity and realizing the initialgeneration of alkali metal at a temperature of about 700 C.

A further combination of alkali metal salts and niobium wherein therewere mixed sodium molybdenate and niobium in the mol ratio Fa/Nb of 2 to0.07 exhibited the same effect as described above.

In addition to the aforementioned kinds of alkali metal salts involvedin the alkali metal generating agents according to the presentinvention, there may be used others alone or in combination. Said othersalts can still display the same effect as mentioned above. There willnow be described the concrete examples where there were used said othersalts in combination.

(D) There is used a mixture of sodium and potassium salts as a source ofalkali metal. The respective salts are mixed in such a manner that themol ratio of the total amount of sodium and potassium salts constitutingsaid source to the niobium is about 1:02 to 50 [(Na-HK/Nb=0.02 to 5)] Itis also experimentally disclosed that when the mol ratio of sodium andpotassium is Na/F=O.1 to 10 the resultant photosensitive layer has goodphotosensitivity.

(E) There are mixed salts of cesium and potassium to form a source ofalkali metal in such a manner that the mol ratio of the total amount ofcesium and potassium salts constituting said source to the niobium isabout 1:02 to [(6s+K)/Nb=0.0l to 5)]. In this case, the cesium andpotassium mixed in the mol ratio of 110.5 to 10' (Es/K=0.l to 20)aifords good results.

(F) There are mixed salts of cesium and sodium as a source of alkalimetal in such a manner that the mol ratio of the total amount of cesiumand sodium salts constituting said source to the niobium is about1:0.125 to 100 Cs+ fia)/Nb=0.01 to 8)]. In this case, too, the

mixing of cesium and sodium in the mol ratio of 1:0.03

to 10 (Es/fia=0.l to 30) displays a .good effect.

The aforementioned metal salts used as a source of alkali metal include,for example, chromates, bichromates, tungstates and molybdenates.

The present invention will be more fully understood fromthe exampleswhich follow:

' EXAMPLES A, B AND C There were mixed powders of cesium chromate,potassium chromate and sodium chromate respectively with powders ofniobium in the mol ratio of 1:2 to form an alkali metal generatingagent. The properties of these mixtures are presented in FIGS. 1A and1B, FIGS. 2A and 2B, and Tables 1 and 2.

.agent 1..

For comparison with the aforementioned generating agent of the presentinvention, there was prepared a reference alkali metal generating agentby adding silicon and zirconium respectively in amounts equal to theaforesaid mol ratio of niobium to the above-described mixed powders ofsodium chromate and potassium chromate.

The alkali metal generating agents of the present invention and priorart were respectively charged into a perforated vessel made of electricconductive metal to form a photosensitive layer or surface. With respectto the above-mentioned three kinds of mixtures including the alkalimetal generating agent of the present invention containing niobium and.the reference generating agents containing silicon and zirconiumrespectively, there was EXAMPLE E investigated the generated state ofsodium and potassium There were mixed powders of cesium chromateandcorresponding to the temperature at which said three potassium chromatein such a manner that the cesium and generating agents where heated, theresults being given in 1 FIGS. 3A and 3B. There are further presented inTable 2 Potassmm contained therem had 3 mol of CS/K=4- below comparativedata on said three mixtures, the con- To said mixture j g added Powdersof niobium dition of a layer during formation and its properties afterin the mol ratio of (Cs-l-K)/Nb=0.1 to form an alkali formation. metalgenerating agent according to the present invention.

TABLE 2 Si-l-NazCrOr Zr+Na CrO4 Alkali metal generating agentNb-I-Na,CrO4+KzCrOz +K2CIO +K1Cl04 Mol radio of components {Na/K=1Na/K=1 NalK=1 (Na+K)/Nb=0.2 (Na+'K)/Zr (Na+K)/Zr Photosensitivity uA/lm.(nznumber of sample)... 100 (n=5) 70 ('n=5) 80 (11:5). Generated stateVery stable Unstable Stable. Temperature of generation, C About 900.....About 900.

Puncture or breakage by melting Never Sometimes. Quite rare. Generatedstate affected by varying preheating Little afieeted NoticeablyAffected.

conditions. afiected. Y Gas evolution before generation of alkalimetal... Very small Prominent. Fairly noticeable.

Control of generated state Easy Ditficult Fairly easy. Getter action ofreductant- Small.. Great Bulk density 0.9 1.8. Addition of butter agentNecessary. Preferred. Possibility of explosion.... None.-- Present.Yield of alkali metal High Low Medium.

When there was added to the alkali metal generating agent of the presentinvention used in this example about percent by weight of tungsten oraluminium oxide on the basis of the total amount of said agent, therewas better controlled the generation of alkali metal or reactionvelocity.

There was further investigated the temperature of generation using thesame materials (mixture of sodium and Next for comparison, there wereprepared reference alkali 40 metal generating agents corresponding tothe prior art agent, using silicon and zirconium respectively as areducing agent in place of niobium with all the components mixed in thesame mol ratio as is used in the present invention. There wasinvestigated the amount of cesium and potassium generated from saidthree kinds of generating potassium) as used in this Example D with themol ratio agents contammg f slhcon i mqmum E of niobium to said mixturevaried. The results are pre- Elvely, the data on Slum potasswm g Presentsented in FIG. 4 wherein the ordinate denotes the tem- 5A d 5Brespectlvely- There'were also tested perature C. required for thegeneration of alkali metal K0 the P P of photosensitiv? layer P p andthe abscissa represents the mol ratio of niobium to 0 these three kindsof generating agents, the results being said mixture. given in Table 3below.

TABLE 3 Si Zr H +CsgCrOr +Cs,CrOr Alkali metal generating agentNb+CSzCIOL+K1Cf04 +K CrO4 +KaQrO| M01 ratio of components {CS/Kai CSIK=4Cs/K=4 (Cs-kK)/Nb=0.1 (Cs+K)/Si= (Cs-i-K)/Z r= 0.1 p 0.1Photosensitivity uA/lm. (nznumber oisample).... 100(n=5) (n =5) (n=5).Generated state Very stable...-.. Unstable Stable.

Temperature of generation, O About 780... About 900 About 900. Punctureor breakage by melting Never Sometimes- Quite rare. Generated stateafleeted by varying preheating Little affected Notieeably Atieeted.

conditions. afiected. Gas evolution before generation of alkalimetal.... Very small Prominent... Fairly y, noticeable.

Control of generated state Easy Dilfieult- Fairly easy. Getter action ofreduetant Bulk density Addition of buffer agent Necessary Preferred.Possibility of explosion None None..... Present. Yield of alkali metalHigh Low Medium.

There is further indicated in FIG. 6 the temperature alkali metal saltto the aforesaid alkali metal salts used required for generation ofcesium and potassium with rein combination. There will now be describeda concrete spect to the mixing ratio of Nb to E s-PK. In this figure,ample Of this case.

the ordinate denotes the temperature required for gen- There were mixedPowders f cesium eliminate eration of said alkali metals and theabscissa represents 2 4), Potassium 'omate (K CrO and sodium h l i of Nbto 6 +K chromate (Na CrO in such a manner that 'Cs, Ti and EXAMPLE F l\a are contained in the mol ratio of 1: 1:1. To said mixture was furtheradded niobium in the mol ratio of There were mlxed powders of cesiumchromate (Cs Cr0 and sodium chromate (Na CrO in the mol ratio of6s/fia=3. To this mixture was added niobium in to form. an alkali metalgenerating agent according to the the mol ratio of (Es,+'fia)/ Nb=1 toform an alkali metal present invention. There were comparatively studiedthe generating agent according to the present invention. Thereproperties of said agent consisting of only one alkali metal were alsoprepared prior art generating agents containing and niobium, namely,Nb=+K W0 or Nb+ NaMoO the silicon and zirconium respectively in the samemanner as results being presented in Table 5 below.

TABLE 6 N b+CSzCrO4 Alkali metal generating agent Nb+K WO4 Nb+NaMoO4+K2C1'O4-i-N8aCIO4 USzKzNa=h1z1 Mol ratio of components K/Nb0.2 Na/Nb-02{(6s+K+Na)/Nb=0'2 9.0

Generated state Very stable-.- Stable Stable.

Temperature of generation, C

Puncture or breakage by melting Never Never Never.

Generated state afieeted by varying preheat- Little afiected Littleaffected- Slightly aflected.

ing condition. Gas evolution before generation of alkali metaL- SmallSmall Small. Control of generated state Very easy- Easy Easy. Additionof butter agent Unnecessary" Unnecessary Unnecessary.

Possibility of explosion None None None.

Yield of alkali metal-.. High.

Bulk density 2.4 2.4 2.4.

in Example B. Data of comparative study on the alkali As mentionedabove, the present invention is characmetal generating agents of thepresent invention and prior terized in that there is mixed niobium withalkali metal art are given in FIGS. 7A and 7B and Table 4 below salts.However, there may be further added to said mixformed in the samearrangement as used in FIGS. 5A and ture a material, for example,zirconium used as a reduc- 5B and Table 3 respectively. The temperatureof generaing agent and/ or gettering material in the prior art. Theretion asociated with FIGS. 7A and 7B is presented in FIG. are presentedin Table 6 below the properties of a zirco- 8 formed in the samearrangement as in FIG. 6. nium containing alkali metal generating agentin com TABLE 4 s1 2 +CsCr04 +CSzCIO4 Alkali metal generating agentNb-i-CSgClO4-l-N3.1CIO4 +N82C1Ol +N8QOIOL Mol ratio oi components[Ci/Naps Cs/Nzpg CSINa=3 "l(os+ya /Nb=1 (os+Na) (Cs-l-N'a)! Si=l Zr=1Photosensitivity A/Im. (nznumber of sample).... 100 (n=6) ('n=5) 80(n=5). Generated state Very stable Unstable Stable. Temperature ofgeneration, C About 780 About 900 About 900. Puncture or breakage bymelting--- Nev Sometimes- Quite rare. Generated state afiected byvarying preheating Little afiected Noticeably Afiected.

conditions. affected. Gas evolution before generation of alkalimetal.... Very small Prominent... Fairly noticeable.

Control of generated state Easy Diflicult Fairly easy. Getter action ofreductant- Bulk density Addition of butter agent Possibility ofexplosion- To the present invention may be applicable a differentparison with those of other agents of the present invenalkali metalgenerating agent prepared by adding another tion.

There will now be described by reference to FIG. 9 the case where thereis actually prepared a photosensitive layer for a special image pickuptube. Numeral 10 is a vessel made of electric conductive metal. Thevessel isprepared by rolling, for example, a thin metal sheet oncecrosswise into a cylindrical body, and spot welding the longitudinaledge portions at a prescribed interval to form a slight gap 12 betweenthe welds 11. The vessel is filled with an alkali metal generating agentaccording to 10 the present invention. After the agnt is charged, thewal of each end of the vessel is pressed airtight. I

There will now be described the case where there was formed theantimony-cesium photosensitive layer of a head-on type photoelectrictube, using an alkali metal 15 generator two alkali metal generatorsfilled with a generating agent consisting of a mixture of powderedcesium chromate and powdered niobium and a generating agent consistingof a mixture of powdered potassium chromate and powdered niobiumrespectively. Each mixture weighed 70 mg. and the mol ratio of thealkali metal salt to niobium was chosen to be 1:2. To the curved lateralinner surface of a glass bulb having a face plate at the front part werefitted each alkali metal generator and a known antimony generator by sobending them as to correspond to the curvature of said lateral innersurface of the glass bulb. To both ends of each of these fittedgenerators are connected lead wires drawn to the outside. Thepreparatory step for forming the aforesaid layer ended by disposingsecondary electron multiplying electrodes known to this particular fieldand an anode at prescribed locations respectively. First, the glass bulbwas fully evacuated and then there was introduced current through saidantimony generator containing an antimony generating agent. Said agentwas heated to a temperature of 520 to 570 C. to release antimony so asto deposit a thin film thereof on the inner surface of said face plateto a prescribed thickness. Thereafter, the two alkali metal generatorsof the present invention were preheated 5 minutes at a temperature of600 C. by introducing current therethrough. The generators were furtherheated to 900 C. to release potassium and cesium. Thus, there wasdeposited a thin cesium-potassium film on said antimony substrat to forma photosensitive layer.

The photosensitive layer prepared as described above had aphotosensitivity of 100 ,ua./lm., showing that it had excellentproperties.

There will now be described the formation of a multialkaliphotosensitive layer used in an X-ray fluorescent multiplying tube.There were prepared three mixtures comprising powders of cesiumchromate, sodium chromate and potassium chromate each blended withpowders of niobium in the mol ratio of 1:2 to form alkali metalgenerating agents. The mixtures cotaining cesium and sodium eachweighing 250 mg. and the mixture containing potassium weighing 200 mg.were separately placed in the aforementioned metal vessels to providealkali metal generators. Each of these generators was put in a knownbulb having a fluorescent face formed at one end and a plate ofinsulating material disposed opposite to said 0 fluorescent face at aclose interval. The generators were preheated 5 to 10 minutes at atemperature of 350 C. Then they were heated to 900 C. to release eachalkali metal so as to form a multialkali photosensitive layer on saidinsulation plate. The resultant photosensitive layers 5 had an excellentphot-osensitivity of 100 ,ua./lm. like that of the preceding case.

What we claim is:

1. An alkali metal generating composition comprising a mixture of analkali metal salt and niobium in -a ratio by weight of salt to niobiumof from about 1:0.1 to about 2. A composition according to claim 1wherein the alkali metal salt is selected from the group consisting ofpotassium tungstate, potassium chromate, cesium chromate, sodiumchromate and sodium molybdate.

3. A composition according to claim 2 wherein the alkali metal salt ispotassium chromate, and wherein the weight ratio of said chromate toniobium is 120.1 to 8.

4. A composition according to claim 2 wherein the alkali metal salt iscesium chromate, and wherein the weight ratio of said chromate toniobium is 1:0.3 to 10.

5. A composition according to claim 2 wherein the alkali metal salt issodium chromate, and wherein the weight ratio of said chromate toniobium is 120.1 to 10.

6. A composition according to claim 1 wherein said alkali metal salt iscesium chromate and which further contains silicon and wherein the molratio of Cs/Nb-i-Si is about 0.2.

7. A composition according to claim 1 wherein said alkali metal salt ispotassium chromate and which further contains zirconium and wherein themol ratio of K/Nb+Zr is about 0.2.

8. A composition according to claim 1 wherein said alkali metal salt iscesium chromate and which further contains silicon, zirconium andtungsten and wherein the mol ratio of Cs/Nb+Si+;Zr+W is about 0.2.

9. A composition according to claim 1 wherein said alkali metal salt isa mixture of cesium chromate, potassium chromate and sodium chromateand, wherein the molar ratio of Cs:K:Na is about 1:1:1.

10. A composition according to claim 1 wherein the alkali metal salt isselected from the group consisting of a first mixture of sodium saltsand potassium salts, a second mixture of cesium salts and potassiumsalts and a third mixture of cesium salts and sodium salts.

11. A composition according to claim 10 wherein the mol ratio of thetotal amount of sodium and potassium salts of said first mixture toniobium is from 1:02 to .50.

12. A composition according to claim 11 wherein the mol ratio of sodiumsalt to potassium salt of said first mixture is from 0.1 to 10.

13. A composition according to claim 10 wherein the mol ratio of thetotal amount of cesium salt and potassium salt of said second mixture toniobium is from 1:0.2 to 100.

14. A composition according to claim 13 wherein the mol ratio of cesiumsalt to potassium salt of said second mixture is from 0.1 to 20.

15. A composition according to claim 10 wherein the mol ratio of thetotal amount of cesium salt and sodium salt of said third mixture toniobium is from 1:0.125 to 10.

16. A composition according to claim 10 wherein the mol ratio of cesiumsalt to sodium salt of said third mixture is from 0.1 to 30.

References Cited UNITED STATES PATENTS 2,154,131 4/1939 Ledever 252181.4X 2,173,258 9/1939 Ledever 252181.4 1,835,118 12/1931 Marden 252--18l.4X3,096,211 7/1963 Davis 2S2-l8l.4 X 3,468,807 9/1969 Spangenberg252-181.4

TOBIAS E. LEVOW, Primary Examiner J. COOPER, Assistant Examiner UNITEDSTATES PATENT CETIHCATE OF ECTIN Patent N 3 658, 713 D d April 25 1972Inventor s YORIKATSU IRISAKA et al It. is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

column 5, line 63 after "metal" insert "salts and niobium, there wereprepared four samples from" Signed and sealed this 5th day of December1972.

(SEAL) Attest:

EDWAED MQFLETCPEEJRG ROBERT GQTTSCHALK ttssting Gfficer Commissinner ofPatents ag UNITED STATES PATENT OFFICE v a CERTIFICATE OF CORRECTIONPatent 3,658,713 Dated April' 125, 1972 IHVQHtQI-(S) YoRIKATsU IRISAKAet al It. is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 5, line 63 after "metal" insert "salts and niobium, there wereprepared four samples from".

Signed and sealed this 5th day of December 1972.

(SEAL) Attest:

EDWARD PLFLETCEFJRJR. Y RQBERT GOITSCHALK Attesting Gfficer Commissionerof Patents

